Structural reorganization of the PPy/DBS films caused by the reduction branch of potentiodynamic polymerization

Polypyrrole/dodecylbenzenesulfonate (PPy/DBS) films were synthesized in aqueous solution by cyclic voltammetry. The polymerization carried out at slow scan rates produces two cathodic peaks on the reduction branch. A single reduction peak was obtained at scan rates higher than 50 mV s⁻¹. Two different polymeric structures have been proposed to explain the observed cathodic splitting. Structure I was associated with the organization reached by slow rate electropolymerization processes. Structure II was obtained when I was permanently modified by electrochemical reduction. Under electrogeneration by potential cycling a constant amount of I is generated on every cycle, providing a constant reduction peak A charge. However, the charge involved in peak B, where structure II is reduced, increases with the cycling. Structure I has a lower energetic content than structure II: it is reduced at lesser cathodic potentials than II. Voltammetric and EDX measurements indicated that a main cationic transport occurred during the redox process of the PPy/DBS. However, a certain amount of Na⁺ cations was not interchanged, since they were stabilized inside the polymer, forming ion pairs with an extra quantity of DBS⁻ anions trapped in the polymer matrix during the polymerization process.     

Electrochemical mineralization of sodium dodecylbenzenesulfonate at boron doped diamond anodes

Results are reported of the electrochemical oxidation of sodium dodecylbenzenesulfonate (SDBS), a common surfactant, at boron-doped diamond anodes. The measured critical micelle concentration (CMC) for SDBS in water at 24 °C was almost 150 mg dm⁻³, but this decreased to almost 30 mg dm⁻³ in 0.1 M sodium sulfate. Cyclic voltammetry of a boron doped diamond (BDD) electrode in aqueous SDBS solutions exhibited oxidation current densities at very positive potentials; however, solutions of monomers at concentrations <CMC gave rise to higher current densities than in higher concentration solutions that formed micelles. Galvanostatic electrolyses, with samples analyzed for Total Organic Carbon (TOC) and Chemical Oxygen Demand (COD), were performed in an electrolytic flow cell without separator, operating in batch recycle mode, using solutions containing SDBS at initial concentrations of 25 and 250 ppm. SDBS in basic media (pH = 12) exhibited lower TOC removal rates than in acidic or neutral solutions, due to concurrent oxidation of dissolved carbonates at potentials less positive than required for water oxidation, as evident in cyclic voltammograms. Decreasing the [electrolyte]/[surfactant] ratio from 200 to 10 increased TOC removal rates. For solutions containing monomers, TOC removal rates also increased with flow rate in the second part of the electrolysis, corresponding to reaction of smaller, fragmented organic compounds. When COD removal from a solution containing SDBS micelles was mass transport controlled, current efficiencies were constant at ca. 50%, due to dimerisation of hydroxyl radical to H₂O₂ and its oxidation to dioxygen.